It has been widely accepted that calcium is an essential element for formation of bone and teeth in animals, including humans. In fact, though calcium is the most abundant mineral in the body, approximately 99% of the body's calcium is found in the bones and teeth providing an exchangeable pool of calcium. The remaining one percent is widely distributed in cells and body fluids and is responsible for the regulation of a number of metabolic functions such as nerve impulse conduction, muscle fiber contraction, hormone secretion, blood coagulation, normal heart beat, activation of enzymes, and maintenance of cell membranes. Additionally, calcium is receiving much attention on the front line of medical science because it has recently been discovered that calcium is one of the most important elements for supporting many life activities. For example, recent observations indicate that calcium deficiency not only induces osteoporosis, but also contributes to such diseases as hypertension, arteriosclerosis, arthritis, diabetes, immunological diseases, colon cancer, and obesity. Therefore, the presence of sufficient amounts of calcium within the body is essential for proper health.
One of the problems associated with calcium supplementation is that all sources of calcium are not equally soluble or bioavailable. In addition, some calcium sources are not as pure as others. For example, calcium carbonate derived from bone meal, oyster shell, or other biological origin contains trace amounts of lead and other minerals. Some calcium carbonates also contain silica. Therefore, it is necessary to take additional amounts of these materials to achieve the same bioavailable calcium level as those taken from synthetic sources of essentially pure calcium. In fact, foods fortified with calcium and calcium supplements are being used more often by U.S. consumers and are generally considered by some researchers to offer the same net effect as calcium found naturally in food.
The most effective order of relative bioavailability or intestinal absorption of various calcium salts is controversial. Nevertheless, there are several known factors that affect the absorption of calcium by the human body. In healthy adults, approximately 30% of calcium contained in their diets is absorbed. However, the absorption of calcium from various foods may range from 10% to 40%. Generally, at higher intakes, the efficiency of the absorption process decreases. This is probably due to the body's ability to control the absorption process based upon the need or lack of need for calcium. However, there are methods of altering the body's control over calcium uptake. For example, vitamin D is known to accelerate the intestinal absorption of calcium.
Many forms of ingested calcium are water insoluble and require specific enzymes for proper digestion. These enzymes extract calcium from food and transport it into the blood stream. However, these transport enzymes are not 100% efficient. This means that the transfer of calcium into the blood stream is an amount that is less than the total ingested inorganic calcium. Additionally, acid solutions enhance the solubility of calcium salts. Indeed, the calcium salts in common vitamins are more soluble under acidic conditions. Much of the digestion of foods takes place in the duodenum where the pH of the gastric juices is low. Since calcium salts are more soluble in an acid pH, much of the absorption takes place in this segment of the gastrointestinal tract.
As stated above, calcium is one of the essential minerals involved in many significant biological processes. Recent medical studies have indicated that a diet containing the U.S. recommended daily allowance (RDA) of calcium may be effective in preventing osteoporosis and possibly, preventing high blood pressure and colon cancer. At the same time, oleaginous or high lipid foods such as margarine, butter, lards, vegetable oil spreads, and plant oil are also a significant part of our daily diet. Therefore, there is great public interest in the consumption of calcium fortified oleaginous foods which contain a relatively high percentage of stable, palatable, and bioavailable calcium.
It has been discovered that the biological transport of metal ions can be significantly enhanced by the use of an amino acid chelate because amino acid chelates are absorbed intact by the mucosal cells (see U.S. Pat. No. 4,863,898). This invention demonstrates that a calcium amino acid chelate has enhanced bioavailability as compared to non-chelated calcium due to the active transport of calcium chelates (CaAAC) out of the digestive tract and into the blood stream.
In the area of animal nutrition, the American Association of Feed Control Officials has issued an official definition for an amino acid chelate which defines an amino acid chelate as, "a metal ion from a soluble salt with amino acids with a mole ratio of one mole of metal to one to three (preferably two) moles of amino acids to form coordinate covalent bonds. The average weight of the hydrolyzed amino acids must be approximately 150 and the resulting molecular weight of chelate must not exceed 800."
Additionally, it is documented that amino acid chelates can be prepared from metal ions which do not come from soluble salts. Ashmead, in U.S. Pat. Nos. 4,599,152 and 4,830,716 discloses methods of preparing pure amino acid chelates using metal sources other than soluble metal salts. In addition, Ashmead also discloses in U.S. Pat. No. 5,516,925, methods of preparing amino acid chelates having improved palatability.
Oleaginous or highly lipid foods such as margarine, butter, lards, vegetable oil spreads, and vegetable oils are a significant part of the human diet. Thus, it would be desirable to provide calcium fortified oleaginous or highly lipid foods, yet maintain the desired palatability and storage stability. However, serious practical difficulties in incorporating calcium salts into oleaginous or highly lipid foods have been encountered because most calcium salts have very low solubility in an oleaginous environment. In addition, with regard to the low bioavailability of calcium salt, it is also known that calcium ions form insoluble salts or soaps with long chain fatty acids resulting from metabolism of fat in the gut. Therefore, there is a great need to provide calcium fortification for oleaginous so that the oleaginous foods remain not only palatable and stable, but that the calcium fortificant remains capable of substantially avoiding the formation of insoluble salts.